1. Field of the Invention
The present invention relates to a laminated heat exchanger employed in a cooling cycle or the like in an air conditioning system for vehicles, which is constituted by laminating tube elements and fins alternately over a plurality of levels and, in particular, relates to a laminated heat exchanger with a structure in which a pair of tank portions are formed on one side of each tube element and an intake portion and an outlet portion for heat exchanging medium are provided at one end in the direction of lamination.
2. Description of the Related Art
In order to respond to the need for further miniaturization of heat exchangers and for improvement in heat exchanging efficiency, the applicant of the present invention developed a heat exchanger whose external shape is as shown in FIG. 1A and has been conducting various research into this heat exchanger. In this heat exchanger, with its core main body formed by laminating tube elements alternately with fins over a plurality of levels, a pair of tank portions provided at one side of each tube element are made to communicate with each other through a U-turn passage portion, and a heat exchanging medium flow path with a plurality of continuous passes is formed in the core main body, as shown in FIG. 15, by making the tank portions of adjacent tube elements communicate as appropriate. An intake portion 4 and an outlet portion 5 for heat exchanging medium are provided at one end in the direction of lamination. In heat exchangers of the existing type, the intake portion 4 is made to communicate with the most upstream pass via a communicating pipe 20, and the outlet portion 5 is made to communicate directly with the pass at the most downstream pass.
In the heat exchanger described above, after the heat exchanging medium flows in through the intake portion 4, the heat exchanging medium enters the most upstream pass via the communicating pipe 20 and after going through a plurality of passes it reaches the most downstream pass before it flows out through the outlet portion 5 which is in communication with the most downstream pass. In the heat exchanger, the unidirectional flow in which the heat exchanging medium moves from the tank side toward the non-tank side or from the non-tank side toward the tank side is considered to be one pass, so that a heat exchanger in which the heat exchanging medium passes through the U-turn passage portions twice during the course of its travel from the intake portion to the outlet portion is referred to as a 4-pass heat exchanger, whereas a heat exchanger in which the heat exchanging medium passes through the U-turn passage portions three times is referred to as a 6-pass heat exchanger.
However, in a laminated heat exchanger with 4 passes as described above, since it is structured so that coolant flows out through one end of the core main body, the coolant tends to concentrate at the tube elements that are located closer to the outlet side (toward one end in the direction of lamination) when it travels from the second pass to the third pass, as shown in FIG. 16A. In other words, from the third pass through the fourth pass, the coolant does not flow readily in the area that is close to a partitioning portion .alpha., which partitions the first pass from the fourth pass. This point is substantiated by measured data that are represented with the broken lines in FIGS. 5A and 5B and FIGS. 10A and 10B, which indicate that the temperature of the passing air in this area is higher than that in other areas. It is to be noted that in FIGS. 5A and 5B and FIGS. 10A and 10B, tube numbers (TUBE No.) refer to the tube element number that is obtained by counting from the end where the intake portion and the outlet portion are provided to a specific tube element. In addition, the passing air temperature (AIR TEMP.) refers to the temperature of air with which heat exchange has been performed at the fins when the air passed between the tube elements, measured at a position 1.about.2 cm from the downstream side end surface of the core main body.
Moreover, in a 6-pass heat exchanger, too, as shown in FIG. 16B, the heat exchanging medium tends to flow while concentrating toward the outlet side away from the partitioning portion .alpha. and, as a result, it can be easily deduced that the temperature of the tube elements at the partitioning portion a in the vicinity of the outlet side and the passing air temperature will be different from those in other areas.